Modern lithium batteries are, as a rule, produced in a vacuum chamber, wherein a substrate is provided with a lithium layer. The lithium layer is formed, for example, through the deposition on the substrate of lithium in the vapor state. Since lithium is highly reactive, contact by the operating personnel after opening the vacuum chamber must be avoided. Even if the excess lithium has been pumped out of the vacuum chamber, it is still possible for lithium particles deposited on the inner wall of the vacuum chamber or on facings and/or maskings to harm the operating personnel.
Methods for the production of lithium batteries are already known in which lithium is converted in a vacuum chamber into vapor, which is subsequently deposited on a substrate (JP 59-060866, JP 2003-007290, JP 2003-234100, JP 2007-207663). Nothing is found in these publications regarding the cleaning of the vacuum chamber.
It is further known to eliminate undesirable depositions on the inside of a coating installation by means of a cleaning gas (JP 2003-229365). However, lithium or alkali metals are herein not listed.
Furthermore, cleaning a process chamber by means of a gas containing O2 is known (US 2007/0163617 A1). Herein the cleaning is carried out at increased temperature and under vacuum. The gas preferably also contains H radicals, since the cleaning process can also be carried out by means of a plasma. However, the walls of the process chamber are cleaned of tungsten and not of lithium or another aggressive material.
A further method for cleaning coating chambers is disclosed in DE 103 38 275 A1. In this method the process chamber is flushed with a conditioned purge gas before a coating process. The purge gas is preferably comprised of O2 and N2 with a humidity value of maximally 30%. The coating chamber is cleaned before the coating process and the coating material is not lithium.
US 2002/0185067 A1 discloses a device and a method for the in situ cleaning of a throttle valve in a CVD system. Here a cleaning gas is introduced which can comprise F2, C2F6, O2 or NF3. Lithium is not discussed.
A cleaning process for a coating chamber is furthermore known in which inter alia N2 and O2 are employed as cleaning gases (EP 1 612 857 A1). These gases are converted to plasma and subsequently serve for cleaning the inner wall of a CVD chamber. High frequency is utilized for the generation of the plasma. However, not Li, but rather Si3N4 or SiO2 are removed.
EP 0 441 368 A discloses a device and a method for eliminating excess material from a PVD chamber. During a cleaning cycle a vacuum is generated in the PVD chamber and a gas mixture with reactive gas is introduced into the PVD chamber. The reactive gas is herein activated through plasma discharge. The objects of the cleaning are also screenings. The eliminated material is Ti, W or Al, not however Li.
The invention addresses the problem of cleaning such parts of a vacuum coating chamber which during the production of thin-film batteries are unintentionally coated, for example maskings, metal lining sheets and the like.